In certain transmission designs, torque converters and one-way clutches are replaced by a starting clutch and a damper to provide advantages in cost, mass and packaging. A starting clutch may be used in an automatic transmission which has a large overall ratio, and wherein the engine power to vehicle mass ratio is not too low for the vehicle to launch.
To launch the vehicle, the starting clutch is slipped for a period of several seconds and the energy created is absorbed into the starting clutch reaction plates and forced cooling oil during the shift. A typical shifting clutch is only slipped for fractions of a second and the energy created is absorbed into the reaction steels during the shift and is distributed to the cooling oil after the shift. Due to the longer shift times of the starting clutch and higher energy, the starting clutch has greater cooling needs than the typical shifting clutch.
When a starting clutch is positioned in series axially with another clutch, the clutch apply member for the starting clutch may be castellated to protrude through the other clutch for applying the starting clutch. The clutch apply member passes through the reaction plates of the other clutch by means of small circumferential sections or fingers extending through excluded sections of the other clutch.
A problem with these designs is that the cooling fluid may leak between the starting clutch and the other clutch rather than passing directly through the starting clutch, thereby limiting the cooling capacity.